Method for producing diamond substrate

Abstract

According to the present invention, a novel diamond substrate of which a main surface is a ｛100｝ plane is created from a single crystal diamond of which a main surface is a ｛100｝ plane. The present invention has: a step for performing preliminary processing on a first starting point 42a and a second starting point 42b respectively set on a first crystal plane 11a and a second crystal plane 11b that form a wedge-shaped structure 12 in which a tip tapers toward the main surface 10a inside a single crystal diamond block 10, among crystal planes forming a ｛111｝ plane; and a step for focusing laser beams B by means of a laser focusing unit 190 forming a first scanning line 41a and a second scanning line 41b due to processing marks from the first starting point 42a and the second starting point 42b in the first crystal plane 11a and the second crystal plane 11b toward the main surface 10a, and connecting the first scanning line 41a and the second scanning line 41b at the tip of the wedge-shaped structure 12 to constitute a scanning line unit 41.

Description

Diamond substrate manufacturing method

[0001] The present invention relates to a method for manufacturing a diamond substrate, and more particularly to a method for manufacturing a diamond substrate by processing a single crystal diamond using a laser beam.

[0002] Conventionally, silicon carbide (SiC) and gallium nitride (GaN) have replaced silicon (Si) as semiconductor materials suitable for power devices, but diamond semiconductors have a higher breakdown field and power control index than these semiconductor materials, and also have the highest thermal conductivity, so they are attracting attention as a next-generation material, and research and development is progressing toward their practical use. Furthermore, nitrogen-vacancy centers (NV centers) in diamond are capable of highly sensitive magnetic detection at room temperature, so there is hope for their application in magnetic sensors, and research in this area is also being conducted (see Patent Document 1).

[0003] Single crystal diamonds, which are expected to be applied to these semiconductors, are synthesized by high-pressure, high-temperature (HPHT) or homoepicapital growth, but these synthesis methods are considered difficult to produce large-area bulk substrates of single crystal diamond for use in semiconductor processes. Therefore, chemical vapor deposition (CVD) methods, which grow single crystal diamond heteroepicapically using single crystal magnesium oxide (MgO) as a base crystal, have been adopted as they have an advantage in producing large-area substrates.

[0004] Diamond substrates are manufactured by slicing a single crystal diamond ingot or a block cut from the ingot to a certain length to a certain thickness using a wire saw with diamond abrasive grains. Because the wire of the wire saw has a diameter of at least several tens of micrometers, when slicing a single crystal diamond ingot or block into diamond substrates, a certain width of the slice along the cut surface is lost as a grinding allowance.

[0005] Also disclosed is a method for producing a diamond substrate from a diamond ingot using laser light (see Patent Document 2). In this method, a laser beam is focused and irradiated to a predetermined depth from the main surface of the diamond ingot, and scanned two-dimensionally to form a modified layer with a modified crystal structure, and the diamond substrate is then peeled off from this modified layer.

[0006] JP 2015-59069 A JP 2020-50563 A

[0007] Diamond single crystals have the property that cleavage tends to proceed along the {111} plane, and when a diamond ingot or block whose main surface is the {100} plane is scanned two-dimensionally with laser light, a modified layer develops on the {111} plane, which is the cleavage plane, and cleavage tends to occur along the {111} plane rather than the {100} plane, making it difficult to create a diamond substrate whose main surface is the desired {100} plane.

[0008] The present invention has been proposed in view of the above-mentioned circumstances, and aims to provide a method for manufacturing a single crystal diamond substrate, which produces a diamond substrate having a {100} plane as its main surface from a single crystal diamond having a {100} plane as its main surface.

[0009] In order to solve the above-mentioned problems, the method for manufacturing a diamond substrate according to this application includes the steps of: arranging a laser focusing unit that focuses laser light so as to face the {100} main surface of a single crystal diamond block; focusing the laser light with the laser focusing unit, and performing pre-processing on first and second starting points that are set on first and second crystal faces, respectively, that form wedge-shaped structures that become thinner at their tips toward the main surface within the single crystal diamond block, among the crystal faces that make up the {111} plane; and focusing the laser light with the laser focusing unit, and forming first and second scan lines by processing marks from the first and second starting points toward the main surface on the first and second crystal faces, respectively, and the first and second scan lines being connected at the tips of the wedge-shaped structures to form scan line units.

[0010] The step of forming the first scan line and the second scan line may include a step of pyrolyzing diamond to form graphitized processing marks and a modified layer including cleavage of the {111} plane around the graphitized processing marks.

[0011] The pre-processing may be processing that forms processing marks at the first starting point and the second starting point, and may be processing that forms first pre-scan lines and second pre-scan lines by processing marks from the first starting point and the second starting point to the tip of the wedge-shaped structure on the first crystal face and the second crystal face, respectively.

[0012] The first and second starting points may be formed at the same depth from the main surface. The scan line unit may be formed as an isosceles triangle with a line segment connecting the first and second starting points as a base and the first and second scan lines as hypotenuses.

[0013] The method may further include the steps of: focusing laser light with a laser focusing unit, and performing other pre-processing on other first starting points on other first crystal faces, which are read as the second starting points, and other second starting points set on other second crystal faces, which are parallel to the first crystal face and the second crystal face, respectively, and which form other wedge-shaped shapes inside the single crystal diamond block and whose tips become thinner towards the main surface; and focusing laser light with the laser focusing unit, and forming other first scan lines and other second scan lines by processing marks from the other first starting points and other second starting points towards the main surface, respectively, on the other first crystal faces and other second crystal faces, and the other first scan lines and other second scan lines are connected at the tips of the other wedge-shaped structures to form other scan line units.

[0014] The step of forming the other first scan lines and the other second scan lines may include a step of pyrolyzing diamond to form graphitized processing marks and a modified layer including cleavage of the {111} plane around the graphitized processing marks.

[0015] The other prior processing may be processing that forms processing marks at the other first starting point and the other second starting point. The other prior processing may be processing that forms other first prior scanning lines and other second prior scanning lines by processing marks from the other first starting point and the other second starting point to the tip of the other wedge-shaped structure on the other first crystal face and the other second crystal face, respectively.

[0016] The method may further include a step of replacing another scan line unit with a scan line unit. The method may further include a step of forming a scan line by splicing together scan line units by repeating the steps of replacing another scan line unit with a scan line unit, replacing the second starting point with another first starting point and forming another second starting point, and forming another first scan line and another second scan line from the other first starting point and the other second starting point to form another scan line unit.

[0017] The method may further include forming a plurality of scan lines parallel to each other inside the single crystal diamond block. The first and second scan lines constituting a scan line unit of the scan lines may be formed on a common crystal plane with the first and second scan lines constituting an adjacent scan line unit.

[0018] The cleavage of the {111} plane formed around the graphitized processing marks in the modified layer formed in each scan line may also extend between adjacent scan lines, forming a modified layer extending along the {100} plane parallel to the main surface.The method may further include a step of dividing the single-crystal diamond block along the cleavage of the {111} plane that has developed between the processing marks in the modified layer.

[0019] According to this invention, it is possible to produce {100} substrates with minimal processing loss from bulk crystals of single crystal diamond having {100} planes as the main surface, and from single crystal diamond ingots or blocks obtained by the HTHP method, thereby improving the yield when manufacturing diamond substrates.

[0020] 1 is a perspective view showing a general configuration of a processing apparatus. FIG. 1 is a schematic view illustrating the {111} plane of a single crystal diamond (100) plane. FIG. 1 is a schematic view illustrating the {111} plane of a single crystal diamond (100) plane. FIG. 1 is a schematic view illustrating a crystal orientation along the {111} plane of a single crystal diamond toward the main surface. FIG. 1 is a schematic view illustrating a crystal orientation along the {111} plane of a single crystal diamond toward the main surface. FIG. 1 is a cross-sectional view illustrating a scan line unit. FIG. 1 is a cross-sectional view illustrating the formation of a scan line unit. FIG. 1 is a cross-sectional view illustrating the formation of a scan line unit. FIG. 1 is a cross-sectional view illustrating the formation of a scan line unit. FIG. 1 is a cross-sectional view illustrating the formation of a scan line unit. FIG. 1 is a cross-sectional view illustrating the formation of a scan line. FIG. 1 is a cross-sectional view illustrating the formation of a scan line. FIG. 1 is a cross-sectional view illustrating the formation of a scan line. FIG. 1 is a cross-sectional view illustrating the formation of a scan line. FIG. 1 is a cross-sectional view illustrating the formation of a scan line. 14 is a photograph showing a scanning line formed by a modified laser beam scanning method. FIG. 15 is a photograph showing a block machined by a modified laser beam scanning method. FIG. 16 is a photograph showing a block machined by a modified laser beam scanning method. FIG. 17 is a photograph showing a surface of a block machined by a modified laser beam scanning method, divided by peeling. FIG. 18 is a photograph showing a surface of a block machined by a modified laser beam scanning method, divided by peeling. FIG. 19 is a schematic diagram showing a laser beam scanning method of an experimental example. FIG. 19 is a schematic diagram showing a laser beam scanning method of an experimental example. FIG. 19 is a schematic diagram showing a laser beam scanning method of an experimental example. FIG. 19 is a photograph showing a processing mark formed according to the scanning method of FIG. 14. FIG. 19 is a photograph showing a processing mark formed according to the scanning method of FIG. 14. FIG. 19 is a photograph showing a processing mark formed according to the scanning method of FIG. 14. FIG. 19 is a schematic diagram explaining a laser beam scanning method of a comparative example.10A and 10B are diagrams illustrating scan lines formed by a laser beam scanning method according to a comparative example, and FIG. 10A are diagrams illustrating scan lines formed by a laser beam scanning method according to a comparative example.

[0021] Next, an embodiment of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are designated by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between thickness and planar dimensions, the thickness ratio of each layer, etc., may differ from the actual ones. Therefore, specific thicknesses and dimensions should be determined with reference to the following description. Furthermore, it goes without saying that the drawings may include parts with different dimensional relationships and ratios.

[0022] Furthermore, the embodiments shown below are merely examples of devices and methods for embodying the technical ideas of this invention, and the materials, shapes, structures, arrangements, etc. of the components of the embodiments of this invention are not limited to those described below. Various modifications can be made to the embodiments of this invention within the scope of the claims.

[0023] 1 is a perspective view showing the general configuration of a processing apparatus 100. The processing apparatus 100 has a stage 110 on which a block 10 of single crystal diamond is placed, a stage support 120 that supports the stage 110 so that it can move in the X and Y directions in a horizontal plane, and a fixture 130 that secures the block 10 of single crystal diamond. The fixture 130 can be an adhesive layer, a mechanical chuck, an electrostatic chuck, a vacuum chuck, or the like.

[0024] On the stage 110, a plate-shaped block 10 having a rectangular periphery, obtained by cutting a single crystal diamond ingot to a predetermined length, is fixed as the workpiece, with the (100) plane, which is the main surface and has an off-angle of 0°, as the upper main surface 10a. In this embodiment, the (100) plane will be described as an example of the {100} plane, but other planes included in the {100} plane can be similarly applied. In addition, the shape of the workpiece is not limited to this, and it may be, for example, a single crystal diamond ingot or a disk-shaped wafer, or a bulk crystal of single crystal diamond, as long as the main surface 10a is similarly the (100) plane.

[0025] The processing apparatus 100 also has a laser light source 160 that generates pulsed laser light, and a laser focusing unit 190 that includes an objective lens 170 and an aberration adjustment unit 180, and irradiates laser light B emitted from the laser light source 160 via the laser focusing unit 190 toward the (100) plane of the main surface 10a of the single-crystal diamond block 10.

[0026] FIG. 2 is a schematic diagram illustrating the arrangement of {111} planes when the crystal structure of a single-crystal diamond block 10 having a (100) plane as its main surface is viewed from the top main surface 10a. FIG. 2A is a top view of the single-crystal diamond block 10, and FIG. 2B is a cross-sectional view of the single-crystal diamond block 10 of FIG. 2A cut along the cutting line IIB-IIB. The orientations of

[110] and [01-1] are also shown in the figure. As shown in FIG. 2A, a square pyramid with a (100) plane as its base has four {111} planes: (111), (1-11), (1-1-1), and (11-1). Furthermore, as shown in FIG. 2B, this {111} plane forms an angle of 55° with respect to the (100) plane. Due to limitations on the characters that can be used in this specification, for convenience, the overscores attached to the numbers in the Miller index notation will be replaced with a negative sign "-" before the numbers. The same applies hereinafter.

[0027] Here, in diamond crystal, carbon atoms are covalently bonded to adjacent carbon atoms by the arms of sp3 hybrid orbitals that extend in the direction of the four vertices of a regular tetrahedron centered on the carbon atom.The carbon atoms that are covalently bonded to the four adjacent carbon atoms form a body-centered cubic lattice called diamond structure.In diamond structure, carbon atoms form covalent bonds with the four adjacent carbon atoms, so single crystal diamond is known to be very hard.However, in the <111> direction, a carbon atom is covalently bonded to one adjacent carbon atom by only one arm of sp3 hybrid orbitals.Therefore, in the {111} plane direction perpendicular to the <111> direction, it can be separated relatively easily by simply cutting the covalent bond of this one arm, and this {111} plane becomes the cleavage plane.

[0028] Fig. 3 is a schematic diagram illustrating the crystal orientation along the {111} plane of a single crystal diamond having a (100) plane as its main surface toward the main surface. Fig. 3A is a top view of a single crystal diamond block 10, and Fig. 3B is a cross-sectional view of the single crystal diamond block 10 of Fig. 3A cut along the cutting line IIIB-IIIB. Fig. 3A shows the crystal orientation along the four (111), (1-11), (1-1-1), and (11-1) planes toward the base of the square pyramid, i.e., toward the main surface 10a of the single crystal diamond block 10 with an off-angle of 0°, and the [2-1-1] direction along the (111) plane, the [21-1] direction along the (1-1-1) plane, the

[211] direction along the (1-1-1) plane, and the [2-11] direction along the (11-1) plane are respectively illustrated. That is, as shown in Figure 3B, the crystal orientation along the {111} plane toward the surface of the single crystal diamond block 10 is <211>.

[0029]

[0030] 4 is a cross-sectional view illustrating a scanning line unit. According to the scanning method of the present embodiment using laser light B, the scanning line formed by laser light B irradiated onto the single crystal diamond block 10 from the laser focusing unit 190 is made up of scanning line units 41. Within the single-crystal diamond block 10, the scan line unit 41 is formed within the crystal planes constituting the {111} plane, with respect to the (1-11) plane of the first crystal face 11a and the (11-1) plane of the second crystal face 11b forming a wedge-shaped structure 12 whose tip becomes thinner toward the (100) plane of the main surface 10a at a first depth D1 from the main surface 10a and whose tip extends in the

[011] direction, such that a first scan line 41a is formed from a first starting point 42a due to a processing mark formed on the first crystal face 11a at a second depth D2 from the main surface 10a toward the main surface 10a in the [21-1] direction, and a second scan line 41b is formed from a second starting point 42b due to a processing mark formed on the second crystal face 11b at the second depth D2 from the main surface 10a toward the main surface 10a in the [2-11] direction, and the first scan line 41a and the second scan line 41b are connected at the tip of the wedge-shaped structure 12.

[0031] The first starting points 42a and the second starting points 42b are formed prior to the formation of the first scan lines 41a and the second scan lines 41b, respectively. The first scan lines 41a and the second scan lines 41b are formed by scanning the laser beam B at the dot pitch DP while converging the laser beam B onto the previously formed first starting points 42a and the second starting points 42b. The first starting points 42a and the second starting points 42b are processing marks formed at the converging points of the laser beam B. These processing marks do not need to be graphitized, but are preferably graphitized to enhance the focusing effect even when the output of the laser beam B is reduced during the scan line formation process. In this embodiment, a crystalline phase transition occurs at the starting points described as the first starting points 42a and the second starting points 42b. Therefore, graphitized processing marks are easily formed by converging the laser beam B onto the starting points during the scan line formation process described as the first scan lines 41a and the second scan lines 41b.

[0032] The first scan line 41a and the second scan line 41b form a modified layer including graphitized processing marks formed at intervals of the dot pitch DP and cleavage along the {111} plane, which is a cleavage plane that occurs around the processing marks due to volume changes caused by the graphite. The processing marks of the first starting points 42a and the second starting points 42b are sometimes referred to as being formed by prior processing because they are formed prior to the first scan line 41a and the second scan line 41b. Prior processing is a process performed to induce a phase transition in the crystal of the light-collecting portion. The phase transition causes a volume change, and the purpose of prior processing is to control the energy applied to the crystal to induce a local phase transition so that this volume change does not cause cleavage along an unexpected crystal orientation to spread.

[0033] In the scan line unit 41, the first scan line 41a extends in the [21-1] direction, and the second scan line 41b extends in the [2-11] direction. The first scan line 41a and the second scan line 41b, which are connected at the tip of the wedge-shaped structure 12, lie in the same plane and form the hypotenuse of an isosceles triangle. This isosceles triangle satisfies the following relational expression (1), where P, which is the distance between the first starting point 42a and the second starting point 42b, is the length of the base, H is the height from the second depth D2 to the first depth D1, and θ is the base angle. As described above, the base angle θ is 55°.

[0034]

[0035] According to this relational expression (1), the starting point pitch P is given by relational expression (1) based on the height H from the second depth D2 to the first depth D1 and the base angle θ. In other words, the second starting point 42b can be formed at a distance from the first starting point 42a in the [01-1] direction of the base by the starting point pitch P given by the height H and the base angle θ. Furthermore, by reducing the height H in relational expression (1), the distance between depths D1 and D2, i.e., the machining area, can be reduced, thereby reducing machining loss.

[0036] Generally, within the block 10 of single crystal diamond having a {100} plane as its main surface 10a, the scan line unit 41 is formed such that, for a first crystal face 11a and a second crystal face 11b among the crystal faces constituting the {111} plane, which form a wedge-shaped structure 12 at a first depth D1 from the main surface 10a, the tip of which becomes thinner towards the {100} plane of the main surface 10a, a first scan line 41a is formed from a processing mark of a first starting point 42a formed on the first crystal face 11a at a second depth D2 from the main surface 10a towards the main surface 10a, and a second scan line 41b is formed from a processing mark of a second starting point 42b formed on the second crystal face 11b at the second depth D2 from the main surface 10a towards the main surface 10a, and the first scan line 41a and the second scan line 41b are connected at the tip of the wedge-shaped structure 12. In this case, too, the first scanning line 41 a and the second scanning line 41 b connected at the tip of the wedge-shaped shape 12 are in the same plane and form the hypotenuse of an isosceles triangle, and when the pitch P of the starting points, which is the distance between the first starting point 42 a and the second starting point 42 b, is defined as the length of the base, the height H is defined as the distance from the second depth D2 to the first depth D1, and the base angle of the isosceles triangle is defined as θ, the relationship shown in relational expression (1) is satisfied.

[0037] 5 is a cross-sectional view illustrating the formation of scan line units 41. As shown in FIG. 5A, within a single-crystal diamond block 10, the (1-11) plane of first crystal face 11a and the (11-1) plane of second crystal face 11b form a wedge-shaped structure 12 whose tip tapers toward the (100) plane of main surface 10a and extends in the

[011] direction. Laser light B is focused on first crystal face 11a from laser focusing unit 190, forming first starting points 42a due to processing marks at a second depth D2 from main surface 10a.

[0038] 5B , following the formation of the first starting points 42a, laser light B is focused from the laser focusing unit 190 on the second crystal face 11b to form second starting points 42b due to processing marks at a second depth D2 from the main surface 10a. As described above, the first starting points 42a and the second starting points 42b correspond to the vertices of the base of an isosceles triangle with the first scanning line 41a and the second scanning line 41b as hypotenuses. Therefore, the second starting points 42b are located at a distance equal to the starting point pitch P from the first starting point 42a in the [01-1] direction perpendicular to the direction in which the tip of the wedge-shaped structure 12 extends. The starting point pitch P is given by the relational expression (1) below, where H is the height from the second depth D2 to the first depth D1 and θ is the base angle of the isosceles triangle.

[0039] 5C , following the formation of the second starting points 42b, laser light B is irradiated from laser focusing unit 190 onto the (1-11) plane of first crystal face 11a to form first scanning lines 41a from the first starting points 42a to the tips of wedge-shaped structures 12. By irradiating the first starting points 42a with the focused laser light B, a modified layer is formed that includes graphitized processing marks in the scanning direction of first scanning lines 41a and cleavage along the (1-11) plane around the processing marks.

[0040] 5D, laser light B is irradiated from laser focusing unit 190 onto the (11-1) plane of second crystal face 11b to form second scan line 41b from second starting point 42b to the tip of wedge-shaped structure 12. Similarly to the above, graphitized regions and cleavage around the second scan line 41b are formed in second scan line 41b. The first scan line 41a and the second scan line 41b are connected at the tip of wedge-shaped structure 12, and a scan line unit 41 formed by connecting first scan line 41a and second scan line 41b is formed.

[0041] Here, the "connected state" refers to a state in which the modified layers constituting the first scan line 41a and the second scan line 41b are connected at the first depth D1. More specifically, in the modified layers of the first scan line 41a and the second scan line 41b, the focal points of the laser light B overlap, the focal points do not overlap and the graphite regions are connected, or neither the focal points nor the graphite regions are connected and the surrounding cleavages are connected. In either state, it is necessary that the first scan line 41a and the second scan line 41b do not extend from the tip of the wedge-shaped structure 12 toward the main surface. This is achieved by optimizing the laser processing conditions and highly accurate processing position control.

[0042] Generally, when the main surface 10a of the single-crystal diamond block 10 is a {100} plane, the laser focusing unit 190 focuses the laser beam B to form first starting points 42a and second starting points 42b due to processing marks on the first crystal face 11a and the second crystal face 11b, respectively, which form the wedge-shaped structure 12 that tapers toward the main surface 10a within the crystal face constituting the {111} plane. The laser focusing unit 190 then focuses the laser beam B to form first scanning lines 41a and second scanning lines 41b due to processing marks on the first crystal face 11a and the second crystal face 11b, respectively, from the first starting points 42a and the second starting points 42b toward the main surface 10a. The first scanning lines 41a and the second scanning lines 41b are connected at the tips of the wedge-shaped structures 12 to form the scanning line units 41.

[0043] 6 is a cross-sectional view illustrating the formation of a scan line, in which a scan line unit 41′ is added to a scan line unit 41 formed in a block 10 of single crystal diamond as shown in FIG.

[0044] As shown in Figure 6A, within the single-crystal diamond block 10, the (1-11) plane of the other first crystal face 11a' and the (11-1) plane of the other second crystal face 11b' are parallel to the (1-11) plane of the first crystal face 11a and the (11-1) plane of the second crystal face 11b, respectively, and form another wedge-shaped structure 12' that tapers toward the (100) plane of the main surface 10a and extends in the

[011] direction. The second starting point 42b is replaced with the other first starting point 42a'. The other first crystal face 11a' is selected so as to pass through the other first starting point 42a'.

[0045] As shown in FIG. 6B , after the replacement of the other first starting point 42a′, laser light B is focused from the laser focusing unit 190 on the other second crystal face 11b′ to form another second starting point 42b′ due to processing marks at a second depth d2 from the main surface 10a. The other first starting point 42a′ and the other second starting point 42b′ correspond to the vertices of the base of an isosceles triangle with the other first scanning line 41a′ and the other second scanning line 41b′ ​​described below as its hypotenuse. Therefore, the other second starting point 42b′ is located at a distance equal to the starting point pitch P from the other first starting point 42a′ in the [01-1] direction perpendicular to the direction in which the tip of the other wedge-shaped structure 12′ extends. As described above, the starting point pitch P is given by the relation (1), where H is the height from the second depth D2 to the first depth D1 and θ is the base angle of the isosceles triangle.

[0046] 6C , following the formation of the other second starting point 42b', laser light B is irradiated from the laser focusing unit 190 on the (1-11) plane of the other first crystal face 11a' to form another first scan line 41a' from the other first starting point 42a' to the tip of the other wedge-shaped structure 12'. Furthermore, laser light B is irradiated from the laser focusing unit 190 on the (11-1) plane of the other second crystal face 11b' to form another second scan line 41b' from the other second starting point 42b' to the tip of the other wedge-shaped structure edge 12'. The other first scan line 41a' and the other second scan line 41b' are connected at the tip of the other wedge-shaped structure 12', and another scan line unit 41' is formed by connecting the other first scan line 41a' and the second scan line 41b'.

[0047] 6D , another scan line unit 41′ is replaced with a scan line unit 41. The other first starting point 42a′, the other second starting point 42b′, the other first scan line 41a′, and the other second scan line 41b′ ​​constituting the other scan line unit 41′ are replaced with a first starting point 42a, a second starting point 42b, a first scan line 41a, and a second scan line 41b, respectively. Similarly, the other first crystal face 11a′, the other second crystal face 11b′, and the other wedge-shaped structure 12′ are replaced with a first crystal face 11a, a second crystal face 11b, and a wedge-shaped structure 12, respectively.

[0048] 6A, in FIG. 6D, within the single-crystal diamond block 10, the (1-11) plane of the other first crystal face 11a' and the (11-1) plane of the other second crystal face 11b' are parallel to each other, forming another wedge-shaped structure 12' whose tip tapers toward the (100) plane of the main surface 10a and extends in the

[011] direction. In the other first crystal face 11a', the second starting point 42b is replaced with another first starting point 42a'. The other first crystal face 11a' is selected so as to pass through the other first starting point 42a'. Then, on the other second crystal face 11b', laser light B is focused from the laser focusing part 190 to form another second starting point 42b' due to a processing mark at a second depth d2 from the main surface 10a. The other second starting point 42b' is located at a distance equal to the pitch P of the aforementioned starting points in the [01-1] direction perpendicular to the other wedge-shaped structure 12', relative to the other first starting point 42a'. Thereafter, the above-described operation is repeated to form another scan line unit 41'. In this way, a scan line is formed by appending another scan line unit 41' to the scan line unit 41.

[0049] Generally, when the main surface 10a of the single-crystal diamond block 10 is a {100} plane, the second starting point 42b is read as the other first starting point 42a' on the other first crystal face 11a' for the other first crystal face 11a' and the other second crystal face 11b' that are parallel to the first crystal face 11a and the second crystal face 11b, respectively, and form another wedge-shaped structure 12' that tapers toward the main surface 10a. The other first crystal face 11a' is selected so as to pass through the other first starting point 42a'. The laser beam B is focused by the laser focusing unit 190, and another second starting point 42b' is formed on the other second crystal face 11b' by a processing mark. Then, laser beam B is focused by laser focusing unit 190 to form another first scan line 41 a' and another second scan line 41 b' due to processing marks on another first crystal face 11 a' and another second crystal face 11 b' from another first starting point 42 a' and another second starting point 42 b' toward main surface 10 a. The other first scan line 41 a' and the other second scan line 41 b' are connected at another edge 12' to form another scan line unit 41'. The other scan line unit 41' formed in this way is read as a scan line unit 41, and a scan line is formed by joining scan line units 41 by forming further another scan line unit 41'.

[0050] FIG. 7 is a perspective view showing the formation of a modified layer on a single-crystal diamond block 10. By forming modified layers constituting scan lines 40 in parallel, a modified layer is formed across the entire main surface 10a of the single-crystal diamond block 10. As shown in FIG. 7, scan line units 41 are added from one end of the single-crystal diamond block 10 to the other end to form the scan line 40. When the scan line 40 reaches the other end of the block 10, the position where the laser light B is irradiated is moved, for example, in the

[011] direction in which the tip of the wedge-shaped structure 12 extends, at a distance of line pitch LP from the scan line 40, and then scan line units 41 are added from the other end of the block 10 to one end to form the scan line 40. By repeating this operation, the scan line 40 is formed across the entire main surface 10a of the block 10 to a predetermined depth.

[0051] Here, in the opposing scan line units 41 of adjacent scan lines 40, the first scan line 41a and the second scan line 41b may be formed on a common crystal plane. For example, the first crystal plane 11a and the second crystal plane 11b on which the first scan line 41a and the second scan line 41b of a scan line unit 41 constituting a certain scan line 40 are formed may be common to the other second crystal plane 11b' and the other first crystal plane 11a' on which the second scan line 41b' and the first scan line 41a' of the opposing scan line unit 41' of another adjacent scan line 40' are formed, respectively. Here, it is taken into consideration that the progression directions in which the scan line units 41 are formed are opposite in a pair of adjacent scan lines 40. When the crystal planes of the adjacent opposing scan line units 41 are common, cleavage is formed between the modified layers constituting the adjacent scan lines 40, progressing across the scan lines 40 along the common crystal plane. The cleavage progresses between the modified layers that form adjacent scan lines 40, so that a modified layer including cleavage is formed over the entire main surface 10a of the block.

[0052] Generally, even when the main surface 10a of the block 10 of single crystal diamond is a {100} plane, the scan line 40 is formed by splicing scan line units 41 from one end of the block 10 to the other end, and when the scan line 40 reaches the other end of the block 10, the position where the laser light B is irradiated is moved in a predetermined direction in which the tip of the wedge-shaped structure 12 extends, spaced apart by the line pitch LP from the scan line 40, and then the scan line 40 is formed by splicing scan line units 41 from the other end of the block 10 to the one end. By repeating this operation, the scan line 40 is formed over the entire main surface 10a of the block 10 to a predetermined depth. Cleavage between the modified layers that make up such scan lines 40 progresses, and a modified layer is formed over the entire main surface.

[0053] 8 is a cross-sectional view showing a modified layer formed on a single-crystal diamond block 10. In the block 10, the modified layer, which includes the processing marks and the surrounding {111} cleavage, forms scan lines 40, and the cleavage also extends between the modified layers that form adjacent scan lines 40, forming modified layers 48. Because the modified layers 48 extend parallel to the (100) plane of the main surface 10a, a substrate that is thinned to a thickness extending from the main surface 10a to the modified layers 48 can be produced by peeling and dividing the block 10 at the modified layers 48.

[0054] Generally, when the main surface 10a of the single-crystal diamond block 10 is a {100} plane, the modified layer 48 is formed parallel to the {100} plane of the main surface 10a. Therefore, by separating the block 10 at the modified layer 48 by peeling, it is possible to produce a substrate that is thinned to a thickness extending from the {100} plane of the main surface 10a to the modified layer 48.

[0055] Figure 9 shows scan lines 40 formed on a block 10 of single crystal diamond by the scanning method of the embodiment using laser light B. Figure 9A is a schematic diagram of the scan lines 40 formed on the formed block 10, and Figure 9B is a photograph of the scan lines 40 formed on the block 10 according to Figure 9A.

[0056] The processing conditions are as shown in Table 2. The first and second starting points 42a and 42b are pre-processed by arranging them at a starting point pitch P and a line pitch LP at a second depth D2 (not shown). Next, the laser beam B is scanned at a dot pitch DP from the first and second starting points 42a and 42b along the (11-1) and (1-11) planes to a first depth D1 (not shown), forming first and second scanning lines 41a and 41b at a line pitch LP. The scanning line units are formed with a starting point pitch P of 140 μm and a height H of 100 μm. In the photograph of FIG. 9B , it can be observed that the scan line units 41 constituting the scan line 40, regardless of whether they are the first scan line 41 a or the second scan line 41 b, have a modified layer of approximately uniform thickness along the scan line 40, including processing marks made of graphite and cleavage around the same, and the cleavage extends between adjacent scan lines 40, connecting the modified layers between the scan lines 40.

[0057]

[0058] (Modification) Next, a modified scanning method of the laser light B will be described. FIG. 10 is a perspective view showing a modified scanning method of the laser light B. In the scanning method of the modified example, as the pre-processing of the first starting point 42a and the second starting point 42b, instead of forming processing marks as shown in FIG. 4, the first starting point 42a and the second starting point 42b form a first pre-scan line 43a and a second pre-scan line 43b from the first starting point 42a and the second starting point 42b to the tip of the wedge-shaped structure 12, respectively. The first pre-scan line 43a and the second pre-scan line 43b are connected at the edge 12 as described above. In the modified example, the first starting point 42a and the second starting point 42b simply serve as starting points for the first pre-scan line 43a and the second pre-scan line 43b.

[0059] Next, first scan lines 41a and second scan lines 41b are formed to overlap the first preceding scan lines 43a and second preceding scan lines 43b up to the tips of the wedge-shaped structures 12, and are connected at the tips of the wedge-shaped structures 12 to form scan line units 41. Here, it is preferable that the dot pitch DP1 of the processing marks forming the first preceding scan lines 43a and second preceding scan lines 43b is larger than the second dot pitch DP2 forming the first scan lines 41a and second scan lines 41b, because this facilitates graphitization due to the presence of starting points.

[0060] Figure 10A is a perspective view showing a first preceding scan line 43a and a second preceding scan line 43b formed over the entire surface of the single crystal diamond block 10. Figure 10B is a perspective view showing a first scan line 41a and a second scan line 41b formed over the entire surface of the single crystal diamond block 10. As described above, the first scan line 41a and the second scan line 41b are formed overlapping the first preceding scan line 43a and the second preceding scan line 43b, and are connected at the tip of the wedge-shaped structure 12 to form a scan line unit 41. As shown in Figure 10A, the first preceding scan line 43a and the second preceding scan line 43b may be formed in advance over the entire main surface 10a of the single crystal diamond block 10, or as described in the steps of Figures 5 and 6, they may be formed one scan line unit 41 at a time, and the scan line 40 may be formed by joining the scan line units 41. Furthermore, for each scan line unit to be formed, the first starting points 42a may be formed continuously at a dot pitch DP1 so as to form a W-shaped cross section. In this manner, the first preceding scan line 43a and the second preceding scan line 43b are formed. The formation of the modified layer 48 according to this modification is similar to that of the embodiment described above.

[0061] Figure 11 is a photograph of scan lines 40 formed on a block 10 of single crystal diamond using a modified scanning method of laser light B. In Figure 11, the line pitch LP of the scan lines 40 is 15 μm, and the processing conditions are as shown in Table 3. In Figure 11, it is observed that graphite is formed with a substantially uniform thickness along the scan line 40, regardless of the first scan line 41a and second scan line 41b of the scan line unit 41 that makes up the scan line 40. It is also observed that cleavage extends between the modified layers that make up adjacent scan lines 40, connecting the modified layers.

[0062]

[0063] Figure 12 is a photograph showing a block 10 of single crystal diamond processed using a modified scanning method of laser light B. Figure 12A shows the case where the line pitch LP of the scan lines 40 shown in the processing conditions of Table 3 is 15 μm, and Figure 12B shows the case where only the line pitch LP of the scan lines 40 is 20 μm under the processing conditions of Table 3. In Figure 12A, where the line pitch LP is 15 μm, it can be observed that the entire surface of the block 10 is blackened, and cleavage has progressed to form a modified layer.

[0064] Figure 13 is a photograph showing the surface of a single crystal diamond block 10 that has been separated by peeling, processed using a modified scanning method of laser light B. Figure 13A shows the bottom surface of the peeled portion, and Figure 13B shows the top surface of the peeled portion. In Figure 13A, which shows the bottom surface of the peeled portion, and Figure 13B, which shows the top surface of the peeled portion, it can be seen that graphite has formed along the peeled surface.

[0065] As mentioned above, when a diamond ingot or block is scanned with a laser beam in two dimensions, a modified layer develops around the traces of processing made of graphite on the {111} cleavage plane, and cleavage occurs on the {111} plane, forming a modified layer. On the other hand, in order to form traces of processing by graphitization, the pulse energy of the laser beam must be sufficiently high, about 1 W, but it is difficult to control the spread of cleavage from the graphite region. Furthermore, if the pulse energy is insufficient, graphitization will not occur.

[0066] In this embodiment, a modified layer is formed by inducing cleavage of the {111} plane from the graphitized processing traces using a small laser beam pulse energy, and the starting point of the pre-processing is utilized to enable control of the cleavage spread in the modified layer. Details will be explained in the following experimental example. Note that the processing conditions in this embodiment were obtained using the processing apparatus of this embodiment, and it goes without saying that appropriate processing conditions will be set depending on the specifications of the processing apparatus. In this case, it is essential to appropriately adjust the pulse energy of the laser beam.

[0067] (Experimental Example) An experimental example will be described regarding the formation of the scanning line 40 in relation to the scanning method of the laser light B. Fig. 14 is a schematic diagram showing the scanning method of the laser light B in the experimental example.

[0068] 14A, in the same manner as in the modified example, in a block 10 of single-crystal diamond, a first preceding scan line 43a is formed at a dot pitch of 4 μm in the [21-1] direction along the (1-11) plane of the first crystal face 11a, and a second preceding scan line 43b is formed at a dot pitch of 4 μm in the [2-11] direction along the (11-1) plane of the second crystal face 11b. After forming the first preceding scan line 43a and the second preceding scan line 43b, the first scanning line 41a and the second scanning line 41b were formed at a dot pitch of 2 μm so as to overlap a portion of the first preceding scan line 43a and the second preceding scan line 43b, respectively. In the experimental example, since the formation of the scan line 40 is the issue, the state in which the first preceding scan line 43a and the second preceding scan line 43b are connected at the tip of the wedge-shaped structure 12 as in the embodiment and modified example is not sought.

[0069] In FIG. 14B, in a single-crystal diamond block 10, first scanning lines 41a were formed at a dot pitch of 2 μm in the [21-1] direction along the (1-11) plane of the first crystal face 11a without forming a starting point, and second scanning lines 41b were formed at a dot pitch of 4 μm in the [2-11] direction along the (11-1) plane of the second crystal face 11b.

[0070] 14C , a reference line 44 was formed at a dot pitch of 2 μm by irradiating a valley extending in the [0-1-1] direction formed by the (1-11) plane of the first crystal face 11a and the (11-1) plane of the first crystal face 11a with laser light B. The reference line 44 was formed by pre-processing, with continuous graphitized processing marks serving as starting points. After forming the reference line 44, a first scanning line 41a was formed at a dot pitch of 4 μm in the [21-1] direction along the (1-11) plane of the first crystal face 11a, and similarly, a first scanning line 41a was formed at a dot pitch of 4 μm in the [2-11] direction along the (11-1) plane of the second crystal face 11b.

[0071] 14D , reference lines 45 were formed at a dot pitch of 4 μm by irradiating laser light B in valleys extending in the [0-1-1] direction formed by the (1-11) plane of first crystal face 11a and the (11-1) plane of second crystal face 11b. Reference lines 45 were formed by pre-processing, with graphitized processing marks intermittently serving as starting points. After forming reference lines 45, first scanning lines 41a were formed at a dot pitch of 4 μm in the [21-1] direction along the (1-11) plane of first crystal face 11a, and then first scanning lines 41a were formed at a dot pitch of 4 μm in the [2-11] direction along the (11-1) plane of second crystal face 11b.

[0072] FIG. 15 is a photograph showing the processing marks of the first scan line 41a in FIG. 14. In FIG. 15, pa, pb, pc, and pd represent processing marks formed when the first scan lines 41a and the second scan lines 41b are alternately formed according to the scanning method of the laser light B in FIGS. 14A, 14B, 14C, and 14D, respectively. In FIG. 15, in pa, the processing marks are graphitized in the first scan line 41a and the second scan line 41b, and a blurred state where cleavage has occurred is observed. In pb, no starting point is formed, so the processing marks are not graphitized in the valleys, but graphitization is observed as each scan line extends. This is thought to be because the formed processing marks begin to act as starting points. In pc, the reference line 44 is graphitized, effectively acting as a starting point, graphitizing the first scan line 41a and the second scan line 41b and causing cleavage to progress. In pd, when the processing marks formed at a dot pitch of 4 μm and the light-converging points of the first scanning line 41 a and the second scanning line 41 b overlap, graphitization of the processing marks and the progression of cleavage are observed.

[0073] FIG. 16 is a photograph showing the processing marks when the first scan line 41a is formed according to the scanning method of laser light B in FIG. 14 . In FIG. 16 , in (pa), graphitization of the first scan line and the wall gap are observed to have progressed along the first crystal face 11a. In (pb), almost no graphitization or cleavage of the first scan line is observed because no initiation points are formed. In (pc), graphitization and cleavage of the first scan line 41a are observed to have progressed along the first crystal face 11a. In (pd), the graphitization and cleavage of the first scan line 41a are observed to be insufficient and not uniform. The results of this experimental example confirm that pre-processed initiation points are effective in graphitizing the processing marks and in generating cleavage spreading from the scan line during scan line processing.

[0074] Figure 17 is a set of photographs comparing the effect of starting points due to pre-processing marks according to the scanning method of laser light B shown in Figure 14. In Figure 17A, a first scan line 41 was formed from a reference line 45 on which starting points due to processing marks were formed at a dot pitch of 4 μm, as shown in Figure 14D. Graphitization and cleavage were observed in the first scan line 41a of pd1 formed from the starting points, but sufficient graphitization or cleavage was not observed in the first scan line 41a of pd2 formed between the starting points. In Figure 17B, a first scan line 41a and a second scan line 41b were formed from a reference line 45 on which starting points due to processing marks were formed at a dot pitch of 4 μm, as shown in Figure 14D, as in Figure 17A. As in FIG. 17A , graphitization and cleavage were observed in the first and second scan lines 41a and 41b of pd1 formed from the starting points, but insufficient graphitization or cleavage was observed in the first and second scan lines 41a and 41b of pd2 formed between the starting points. In FIG. 17C , the first and second scan lines 41a and 41b were formed from a reference line without any processing marks, as in FIG. 14B . Insufficient graphitization or cleavage was observed in the first and second scan lines 41a and 41b. These experimental results from FIGS. 17A to 17C reveal that sufficient graphitization and cleavage were obtained when scan lines were formed from processing marks, but insufficient graphitization or cleavage was obtained when scan lines were not formed from processing marks.

[0075] (Comparative Example) As a comparative example, a scanning method of laser light B in which pre-processing is not performed on the first starting point 42a and the second starting point 42b will be described. Fig. 18 is a schematic diagram showing a scanning method of laser light B in the comparative example. In the comparative example, the first starting point 42a and the second starting point 42b are not formed by processing marks, and the first pre-scan line 43a and the second pre-scan line 43b starting from the first starting point 42a and the second starting point 42b are not formed. The comparative example is similar to the scanning method of laser light B in the embodiment, except that pre-processing is not performed.

[0076] Figure 19 shows a scan line 40 formed on a block 10 of single crystal diamond by a comparative example scanning method using laser light B. Figure 19A is a schematic diagram of the scan line 40 formed on the block 10, and Figure 19B is a photograph of the scan line 40 formed on the block 10 according to Figure 19A. The scan line 40 is made up of a first scan line 41a and a second scan line 41b.

[0077] The processing conditions are shown in Table 4. In FIG. 19A, laser light B scans in the direction of the arrow, and the first scan line 41a, indicated by the thin arrow, is formed before the second scan line 41b, indicated by the thick arrow. As an example, in L1, the first scan line 41a on the (1-11) plane is formed, followed by the second scan line 41b on the (11-1) plane. The scan line 40 is formed from the aforementioned second depth D2 at H = 15 μm. In the photograph in FIG. 19B, within the scan line units 41 that make up the scan line 40, graphite and cleavage spreading to the surrounding area are observed in the second scan line 41b, which was processed later. On the other hand, the first scan line 41a, which was processed earlier, shows insufficient graphitization and cleavage progression. This is because a processing mark is present at the starting point at the second depth D2 of the second scan line 41b, which was processed later, while no processing mark is present at the starting point of the first scan line 41a, which was processed earlier.

[0078]

[0079] Although the embodiments and experimental examples have been described above, these embodiments and experimental examples are merely examples for embodying the technical ideas of the present invention, and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. This application claims priority based on Japanese Patent Application No. 2023-121832 filed on July 26, 2023, the entire contents of which are incorporated herein by reference.

[0080] 10 Block 10a Main surface 40 Scan line 41 Scan line unit 41a First scan line 41b Second scan line 42a First starting point 42b Second starting point 43a First preceding scan line 43b Second preceding scan line 44, 45 Reference line 100 Processing device 190 Laser focusing unit

Claims

1. A method for manufacturing a diamond substrate, comprising the steps of:

1. Positioning a laser focusing unit that focuses laser light so as to face a main surface {100} plane of a single crystal diamond block; focusing the laser light with the laser focusing unit, and performing pre-processing on a first starting point and a second starting point that are respectively set on a first crystal face and a second crystal face that form a wedge-shaped structure inside the single crystal diamond block and whose tip becomes thinner toward the main surface, among the crystal faces that constitute a {111} plane; and focusing the laser light with the laser focusing unit, and forming a first scan line and a second scan line by processing marks from the first starting point and the second starting point, respectively, toward the main surface on the first crystal face and the second crystal face, and the first scan line and the second scan line are connected at the tip of the wedge-shaped structure to form a scan line unit.

2. A method for manufacturing a diamond substrate as described in claim 1, wherein the step of forming the first scan line and the second scan line includes a step of forming a modified layer including a processing mark graphitized by thermally decomposing diamond and a cleavage of the {111} plane around the processed mark.

3. A method for manufacturing a diamond substrate as described in claim 1 or 2, wherein the pre-processing is a process for forming processing marks on the first starting point and the second starting point.

4. A method for manufacturing a diamond substrate as described in claim 1 or 2, wherein the pre-processing is a process for forming a first pre-scan line and a second pre-scan line by processing marks from the first starting point and the second starting point to the tip of the wedge-shaped structure on the first crystal face and the second crystal face, respectively.

5. A method for manufacturing a diamond substrate as described in claim 1 or 2, wherein the first starting point and the second starting point are formed at the same depth from the main surface.

6. A method for manufacturing a diamond substrate as described in claim 5, wherein the scanning line unit is formed as an isosceles triangle with a line segment connecting the first starting point and the second starting point as its base and the first scanning line and the second scanning line as its hypotenuse.

7. A method for manufacturing a diamond substrate as set forth in claim 1, further comprising the steps of: focusing laser light by said laser focusing unit, and performing another pre-processing on another first starting point in said other first crystal face, which is replaced with the second starting point, and another second starting point set on said other second crystal face, for another first crystal face and another second crystal face that are parallel to said first crystal face and said second crystal face, respectively, and form another wedge-shaped structure inside said single-crystal diamond block, the tip of which becomes thinner toward said main surface; focusing laser light by said laser focusing unit, and forming another first scan line and another second scan line by processing marks from said other first starting point and said other second starting point toward said main surface, respectively, on said other first crystal face and said other second crystal face, and said other first scan line and said other second scan line are connected at the tip of the other wedge-shaped structure to form another scan line unit.

8. A method for manufacturing a diamond substrate as described in claim 7, wherein the step of forming the other first scan line and the other second scan line includes a step of forming a modified layer including a processing mark graphitized by pyrolyzing diamond and a cleavage of the {111} plane around the processing mark.

9. A method for manufacturing a diamond substrate as described in claim 7 or 8, wherein the other preliminary processing is processing for forming processing marks on the other first starting points and the other second starting points.

10. A method for manufacturing a diamond substrate as described in claim 7 or 8, wherein the other preliminary processing is processing for forming other first preliminary scan lines and other second preliminary scan lines by processing marks from the other first starting point and the other second starting point to the tip of the other wedge-shaped structure on the other first crystal face and the other second crystal face, respectively.

11. A method for manufacturing a diamond substrate as described in claim 7 or 8, further comprising a step of replacing the other scanning line unit with the scanning line unit.

12. A method for manufacturing a diamond substrate as described in claim 7 or 8, further comprising a step of forming a scan line by splicing together the scan line units by repeating the steps of: replacing the other scan line unit with the scan line unit; replacing the second starting point with another first starting point and forming another second starting point; and forming another first scan line and another second scan line from the other first starting point and the other second starting point to constitute the other scan line unit.

13. The method for producing a diamond substrate according to claim 12, further comprising the step of forming a plurality of said scanning lines in parallel to each other inside said single crystal diamond block.

14. A method for manufacturing a diamond substrate as described in claim 13, wherein the first scanning line and the second scanning line constituting the scanning line unit of the scanning line are formed on a common crystal plane as the first scanning line and the second scanning line constituting an adjacent scanning line unit.

15. A method for producing a diamond substrate as described in claim 14, in which the graphitized processing marks of the modified layer formed on each scan line and the cleavage of the {111} planes around them extend between adjacent scan lines, forming a modified layer extending along the {100} planes parallel to the main surface.

16. The method for producing a diamond substrate according to claim 15, further comprising a step of dividing the single crystal diamond block along a cleavage of a {111} plane that develops between processing marks in the modified layer.

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